Cell Structure - Cytoskeleton,ECM, and Cell Junctions

Question 1

What is the Eukaryotic cytoskeleton and what are its functions?

Answer 1

Long filamentous proteins which provide structure, organisation, cell movement/division and exocytosis/endocytosis

Question 2

Where is the cytoskeleton present?

Answer 2

It is present in the cell cortex, cytosol, and nucleoplasm.

Question 3

What three components make up the cytoskeleton?

Answer 3

1.Intermediate filaments
2.Actin Filaments
3.Microtubules

Question 4

What are intermediate filaments?

Answer 4

Stable filaments found throughout the cytoplasm and nucleus.

Also anchored to cell-cell junctions (desmosomes) and cell-matrix junctions (hemidesmosomes)

Question 5

Describe Intermediate filaments and where they are enriched?

Answer 5

Approx 10nm and rope like for tensile strength.

Enriched in cells with high mechanical stress like muscle cells, nerve cell axons and skin epithelia

(also strengthens nuclear membrane)

Question 6

What are the four main classes of intermediate filaments?

Answer 6

1.Keratins (epithelia)
2.Vimentin (connective tissues)
3.Lamins (nucleus)
4.Neurofilaments (nerve cell axons)

Question 7

Describe microtubules and their functions?

Answer 7

Long hollow stiff tubes which extend from the centrosome.

Cellular scaffolding that also acts as a highway for movement of vesicles and other cell components.

Question 8

Name four specific roles of microtubules

Answer 8

1.Migration of chromosomes
2.Cell movement (flagella/cilia)
3.Organelle structure
4.exo/endocytosis

Question 9

Describe microtubules structure in detail

Answer 9

Alpha and beta tubulin stacked to form protofilaments

13 protofilaments form a 25nm hollow microtubules

Question 10

Explain microtubules polarity

Answer 10

The - end towards centrosome has alpha tubulin (slow growth)

+ end towards outside has beta tubulin (fast growth)

(Provides directionality to intracellular transport)

Question 11

Describe centrosome and its functions

Answer 11

The main MTOC enriched in gamma tubulin
Provides anchoring for the mtubule network

Nucleation site

Question 12

What two inhibitors are there to tackle microtubules dynamic instability?

Answer 12

Taxol and Vincristine

Question 13

Where else can MTOCs be found?

Answer 13

Cilia and Flagella contain MTOCs

Question 14

Where is Actin filaments, the most abundant cellular protein, found?

Answer 14

In all Eukaryotic cells and enriched around the PM and holds cell shape

Question 15

What are main functions of actin filaments?

Answer 15

They are essential for cell movement and anchorage

The lamellipodia and filopodia help with movement and antennae

Also used for muscle
Contraction/ cytokinesis

Question 16

Describe the structure of actin filaments

Answer 16

Thin and flexible (helical) 7nm diameter
And can rapidly polymerise and depolymerise like that vid

Can form permanent structures like microvilli

Globular actin forms a double helix chain with a plus and minus end

Question 17

What is a motor protein and give an example?

Answer 17

Motor protein are actin filaments used in muscle contraction

Myosin moves towards plus side of actin filament via Ca2+ and ATP to contract muscle

Question 18

What is the extracellular matrix and its components?

Answer 18

Part of support tissue for almost all organs

Composed of:
Collagen
Elastic fibres
GAG
Proteoglycans, glycoproteins and growth factors

In connective cells and epithelial cells

Question 19

What are the types of cell-cell junctions (epithelial cells)?

Answer 19

3 types of cell-cell junctions:
1.Tight junctions (ensure cell-cell cohesion at the apical membrane
2.Adherens junctions (maintaining cell shape and also desmosomes)
3.Gap junctions (channel for cell-cell communication and pH and calcium dependant opening for channel)

Question 20

What are the 2 types of cell-matrix junctions?

Answer 20

1.Focal adhesion - cell anchorage/stress fibres

2.Hemidesmosomes - attaches cell to ECM